It is often desirable in power transmitting equipment to couple and decouple two shafts. This may be accomplished by sliding an internally-splined collar over its mating externally-splined shaft. To assist the mesh, the leading edge of each spline is usually pointed or rounded to guide the internal spline past the external spline. But some relative rotation is also necessary unless the splines are lined up before engagement. This relative rotation is preferably just enough to allow one tooth to slide past another, since any rotation in excess of this results in unnecessary backlash.